1. Field of the Invention
The present invention is in the field of medicinal chemistry. In particular, the invention is directed to novel heterocyclic amidines and their use for inhibiting the enzyme C1s, a protease in the classical pathway of the complement system; and the use of this inhibition to treat or ameliorate acute or chronic disorders in mammals.
2. Related Art
The immune system of the human body is equipped with several defense mechanisms to respond to bacterial, viral, or parasitic infection and injury. One such defense mechanism involves the complement system. Complement consists of a complex series of approximately 30 plasma and membrane protein components, many of which are proteinases. Once activated, this system of enzymes non-specifically complements the immunologically specific effects of antibody by modulating the immune response, lysing target cells, stimulating vascular and other smooth muscle cells, facilitating the transport of immune complexes, producing anaphylatoxins which cause degranulation of mast cells and release of histamine, stimulating chemotaxis (migration) of leukocytes toward the area of complement activity, activating B lymphocytes and macrophages, and inducing phagocytosis and lysis of cells (Eisen, H. N., Immunology, Harper & Row Publishers, Inc., Hagerstown, Md., p. 512 (1974); Roitt, I. et al., Immunology, Gower Medical Publishing, London, N.Y., pp. 7.1–7.14 (1985); U.S. Pat. Nos. 5,472,939 and 5,268,363).
The complement system functions as a “cascade.” The enzyme cascades are initiated when inactive enzyme precursor molecules are activated, through limited proteolysis, by membrane-bound enzymes. A small fragment is lost from the enzyme precursor and a nascent membrane binding site is revealed. The major fragment then binds to the membrane as the next functionally active enzyme of the complement cascade. Since each enzyme is able to activate many enzyme precursors, the system forms an amplifying cascade, resembling the reactions seen in blood clotting and fibrinolysis (Roitt, I. et al., Immunology, Gower Medical Publishing, London, N.Y., pp. 7.1–7.14 (1985)).
The proteins of the complement system form two inter-related enzyme cascades, termed the classical and alternative pathways. The classical pathway is usually initiated by antigen-antibody complexes, while the alternative pathway is activated by specific polysaccharides, often found on bacterial, viral, and parasitic cell surfaces. The classical pathway consists of components C1–C9, while the alternative pathway consists of components C3–C9 (excluding C4) and several factors, such as Factor B, Factor D, and Factor H.
The sequence of events comprising the classical complement pathway consists of three stages: recognition, enzymatic activation, and membrane attack leading to cell death. The first phase of complement activation begins with C1. C1 is made up of three distinct proteins: a recognition subunit, C1q, and the serine proteinase subcomponents, C1r and C1s, which are bound together in a calcium-dependent tetrameric complex, C1r2s2. An intact C1 complex is necessary for physiological activation of C1 to result. Activation occurs when the intact C1 complex binds to immunoglobulin complexed with antigen. This binding activates C1s which then cleaves both the C4 and C2 proteins to generate C4a and C4b, as well as C2a and C2b. The C4b and C2a fragments combine to form the C3 convertase, which in turn cleaves C3 to form C3a and C3b (Makrides, Pharmacol. Rev. 50:59–87 (1998); and U.S. Pat. No. 5,268,363). Both the classical and alternative pathways are capable of individually inducing the production of the C3 convertase to convert C3 to C3b, the generation of which is the central event of the complement pathway. C3b binds to C3b receptors present on neutrophils, eosinophils, monocytes and macrophages, thereby activating the terminal lytic complement sequence, C5–C9 (Roitt, I. et al, Immunology, Gower Medical Publishing, London, N.Y., pp. 7.1–7.14 (1985)).
Complement is designed to fight infection and injury; however, this same mechanism, if inappropriately activated, can cause a significant amount of inflammation and tissue damage as a result of the rapid and aggressive enzyme activity. Complement-induced inflammation and tissue damage has been implicated in a number of disease states, including: the intestinal inflammation of Crohn's disease which is characterized by the lymphoid infiltration of mononuclear and polymorphonuclear leukocytes (Ahrenstedt et al., New Engl. J. Med. 322:1345–9 (1990)), thermal injury (bums, frostbite) (Gelfand et al., J. Clin. Invest. 70:1170 (1982); Demling et al., Surgery 106:52–9(1989)), hemodialysis (Deppisch et al., Kidney Inst. 37:696–706 (1990); Kojima et al., Nippon Jenzo Gakkai Shi 31:91–7 (1989)), post pump syndrome in cardiopulmonary bypass (Chenoweth et al., Complement. Inflamm. 3:152–165 (1981); Chenoweth et al., Complement 3:152–165 (1986); Salama et al., N. Engl. J. Med. 318:408–14 (1988)), and ischaemia (Huang et al., Science 285:595 (1999); Naka et al., Transplantation 64:1248 (1997); Pemberton et al., J. Immunol. 150:5104 (1993); Chavez-Cartaya et al., Transplantation 59:1047 (1995); Hill et al., J. Immunol. 149:1723 (1992); Weisman et al., Science 249:146 (1990)). Both complement and leukocytes are reported to be implicated in the pathogenesis of adult respiratory distress syndrome (Zilow et al., Clin. Exp. Immunol. 79:151–57 (1990); Langlois et al., Heart Lung 18:71–84 (1989)). Activation of the complement system is suggested to be involved in the development of fatal complications in sepsis (Hack et al., Am. J. Med. 86:20–26 (1989)) and causes tissue injury in animal models of autoimmune diseases such as immune-complex-induced vasculitis (Cochrane, Springer Seminar Immunopathol. 7:263 (1984)), glomerulonephritis (Couser et al., Kidney Inst. 29:879 (1985)), type II collagen-induced arthritis (Watson & Townes, J. Exp. Med. 162:1878 (1985)), and experimental allergic neuritis (Feasby et al., Brain Res. 419:97 (1987)). The complement system is also involved in hyperacute allograft and hyperacute xenograft rejection (Knechtle et al., J. Heart Transplant 4(5):541 (1985); Guttman, Transplantation 17:383 (1974); Adachi et al.,Trans. Proc. 19(1):1145 (1987)). Complement activation during immunotherapy with recombinant IL-2 appears to cause the severe toxicity and side effects observed from IL-2 treatment (Thijs et al., J. Immunol. 144:2419 (1990)).
Complement fragments generated by the classical portion of the complement cascade have been found to be present in the immune complexes formed against indigenous tissue in autoimmune diseases. Such diseases include, but are not limited to: Hashimoto's thyroiditis, glomerulonephritis and cutaneous lesions of systemic lupus erythematosus, other glomerulonephritides, bullous pemphigoid, dermatitis herpetiformis, Goodpasture's syndrome, Graves' disease, myasthenia gravis, insulin resistance, autoimmune hemolyic anemia, autoimmune thrombocytopenic purpura, and rheumatoid arthritis (Biesecker et al. J. Exp. Med. 154: 1779 (1981); Biesecker et al., N. Engl. J. Med. 306: 264 (1982); Falk et al., Clin. Research 32:503A (Abstract) (1984); Falk et al., J. Clin. Invest. 72:560 (1983); Dahl et al., J. Invest. Dermatol. 82:132 (1984); Dahl et al., Arch. Dermatol. 121:70 (1985); Sanders et al., Clin. Research 33:388A (Abstract) (1985); and U.S. Pat. Nos. 5,268,363 and 4,722,890).
Compounds that potently and selectively inhibit complement will have therapeutic applications in several acute and chronic immunological and non-immunological disorders, and a variety of neurodegenerative diseases. Evidence from both human and animal studies shows that activation of the classical complement pathway is primarily involved in neurodegenerative diseases of the central nervous system (CNS). Autoimmune diseases in which these inhibitors of the complement cascade system will be therapeutically useful include myasthenia gravis (MG), rheumatoid arthritis, and systemic lupus erythematosus. Neurodegenerative diseases in which inhibitors of the complement cascade system will be therapeutically useful include the demyelinating disorder multiple sclerosis (MS), the neuropathies Guillain-Barré syndrome (GBS) and Miller-Fisher syndrome (MFS), Alzheimer's disease (AD), and prion-related disease (variant Creutzfeld Jacob disease). Other diseases and conditions include hereditary and acquired angioedema (in which a deficiency in complement inhibitory protein leads to an active complement consumption and repeated episodes of life-threatening angiodema), septic shock, paroxysmal nocturnal hemoglobinuria, organ rejection (transplantation), bums (wound healing), brain trauma, soft tissue trauma, asthma, platelet storage, hemodialysis, ischemia-reperfusion injury, and cardiopulmonary bypass equipment (Makrides, Pharmacol. Rev. 50:59–87 (1998); Spiegel et al., Strategies for Inhibition of Complement Activation in the Treatment of Neurodegenerative Diseases in: Neuroinflammation: Mechanisms and Management, Wood (ed.), Humana Press, Inc., Totowa, N.J., Chapter 5, pp. 129–176; and U.S. Pat. No. 4,916,219).
A number of strategies have been proposed for the inhibition of primarily the classical complement pathway. Efforts to directly inhibit complement activation have focused on chemical compounds that inhibit complement components such as C1r and C1s. Small peptide inhibitors of convertases, such as the C3 and C5 convertases, have also been described (Liszewski and Atkinson, Exp. Opin. Invest. Drugs 7: 323–332 (1998). So far, the best studied ‘designer’ complement inhibitor for treatment of CNS disorders is soluble recombinant human complement receptor Type 1 (sCR1). sCR1 has proven effective in animal models of CNS diseases and is under investigation for use in man (Fearon, Clin. Exp. Immunol. 86 (Suppl.1):43–46 (1991)). However, there are several drawbacks to the use of sCR1 in disorders of the CNS: the agent is expensive, must be administered systemically, and has a short half-life in vivo. The next generation of complement inhibitors are likely to solve many of these drawbacks (Spiegel et al., Strategies for Inhibition of Complement Activation in the Treatment of Neurodegenerative Diseases in: Neuroinflammation: Mechanisms and Management, Wood (ed.), Humana Press, Inc., Totowa, N.J., Chapter 5, pp. 129–176).
A need continues to exist for non-peptidic compounds that are potent inhibitors of complement, specifically C1s, and which possess greater bioavailability and fewer side-effects than currently available C1s inhibitors. Accordingly, novel C1s inhibitors, characterized by potent inhibitory capacity, are potentially valuable therapeutic agents for a variety of conditions.